_Hawassa_Geography_book (1) (1)-1.pdf

Geography of Ethiopia and the Horn (GeES 1011)
Instructor: Tafesse Matewos (PhD)
2019/20 A.Y
Hawassa University GeES 1011
1

Unit 1 Introduction
Unit Contents
1.1. Definition, Scope and Themes of Geography
1.2 Location, Shape and Size of Ethiopia and the Horn
1.3. Basic Skills of Map Reading
2

Chapter One
Chapter Objectives
At the end of this chapter you are expected to:
1. Comprehend the meaning and scope of Geography.
2. Explain the themes of Geography.
3. Explicate the implications of location, shape and size
of Ethiopia and the Horn on the physical environment,
socioeconomic and political aspects.
4. Acquire basic skills of map reading.
3

CHAPTER ONE
INTRODUCTION
 Geography: Definition, Scope and Themes
1.1.1. Meaning of Geography
 It is difficult to forward a definition acceptable to all geographers at all
times and places because of the dynamic nature of the discipline and the
changes in its scope and method of study.
4

Cont’d …
 However, the following may be accepted as a working definition.
 Geography is the scientific study of the Earth
 It describes and analyses spatial and temporal variations of physical, biological
and human phenomena, and their interrelationships and dynamism over the
surface of the Earth.
1.1.2. The Scope, Approaches and Themes of Geography
 Geography is the science that explains:
 the arrangements of various natural and cultural features on the Earth
surface.
 It is a holistic and interdisciplinary field contributing to:
 the understanding of the changing spatial structures from the past to
the future.
5

Cont’d . . .
 In its scope, it ranges from the physical sciences of Astronomy, climatology, Geology
through natural histories of Botany and Zoology to the human studies of Anthropology,
Ethnology, Sociology and History.
 Geography can be approached by considering two continuums:
a physical-human continuum and,
a topical-regional continuum.
6

Cont’d . . .
 The topical (systematic) continuum: the study of one particular topic of
physical or human analysis as it varies from place to place. Examples
would include such topical approaches as Economic Geography, Cultural
Geography, and Urban Geography.
 The Regional Continuum: The study of a particular region, both its human
and environmental attributes. Geographers tend to focus their interests on
certain regions, like East Africa or Africa, as an example.
Five Fundamental and Unifying Themes in Geography
 Geography has five basic themes namely location, place, human-
environment interaction, movement, and region.
7

Cont’d . . .
a) Location
Two types of location-
– Relative
– Absolute
– Relative Location: is based on the location of some physical or human
created feature. Where something is located is based on the location of
other things.
– Absolute Location: Based on a coordinate grid system that gives a
precise location on the earth's surface. The most common coordinate
grid system used is the latitude-longitude coordinate grid system found
on most maps and globes.
8

Cont’d . . .
b)Place
– Place refers to the physical and human aspects of a location.
– This theme of geography is associated with toponym (the name of a
place), site (the description of the features of the place), and situation
(the environmental conditions of the place).
– Each place in the world has its unique characteristics expressed in terms
of landforms, hydrology, biogeography, pedology, characteristics and
size of its human population, and the distinct human cultures.
– The concept of “place” aids geographers to compare and contrast places
on Earth.
9

Cont’d . . .
C) Human-Environment Interaction
 Humans have always been on ceaseless interaction with their natural
environment.
 Human-environment interaction involves three distinct aspects:
dependency, adaptation, and modification.
Dependency: refers to the ways in which humans are dependent on
nature for a living.
Adaptation: relates to how humans modify themselves, their lifestyles
and their behavior to live in a new environment with new challenges.
Modification: allowed humans to “conquer” the world for their
comfortable living.
10

Cont’d . . .
d) Movement
 It entails to the translocation of human beings, their goods, and their ideas
from one end of the planet to another.
 It includes:
The physical movement of people
Transport of goods and services
flow of ideas that allows the unification of the human civilization
and promotes its growth and prosperity.
e) Region
 Is an area of the earth’s surface with similar characteristics.
11

Cont’d . . .
 Regions usually have more than one characteristic that unifies them.
These may include physical, political, economic or cultural characteristics.
 Geographers categorize regions into three:
a) Formal (Uniform) Regions: characterized by a common human
property. E.g. presence of people who share a language, religion,
nationality, and political identity; and common physical property such as
climate, landform, vegetation. They are based on measurable data.
b) Functional (Nodal) regions: are regions that is made up of different
places that are linked and function as a unit.
Usually a functional region is characterized by a hub or central place,
and defined by the linkages binding particular phenomena.
E.g. Addis Ababa is the center of Ethiopia linked with other regions.
12

Cont’d . . .
C) Perceptual Regions
 Is a region in which people perceive, or see the characteristics of a region
in the same way.
 These regions are based on human feelings and attitudes.
 E.g. “Piassa” is the middle of Addis Ababa.
13

1.2 Location, Shape and Size of Ethiopia and the Horn
 Location of Ethiopia
 Astronomical location /mathematical location/,
– Ethiopia located:
– 30N (Moyale) – 150N(Badme) Latitude (North-South120)
– 330E (Akobo) to 480E (the tip of Ogaden) (East- West 150 )
• East - West distance (150 ) is longer than the North - South distance
(120).
14

Cont’d . . .
 Relative location:
Vicinal location In relation to water bodies & land
masses
Sudan to the west and northwest Southwest of the Arabian Peninsula
South Sudan to southwest Northwest of the Indian Ocean
Djibouti to the east In the Nile Basin
Somalia to the east and southeast
Eritrea to the north and northeast
Kenya to the south
15

16

Cont’d . . .
The implications of Ethiopian location, Size, shape
a) Climate
 30N and 150N (between the Equator and Tropic of Cancer) implies that the
country has a tropical climate, though modified by its altitude.
 The location of Ethiopia relative to the Indian Ocean, the Atlantic Ocean and the
African and Asian landmass has also various bearings on the climate of Ethiopia.
b) Socio-cultural
 Ethiopia is one of the earliest recipients of the major world religions namely
Christianity,
Islam and
Judaism
• This due to its proximity to the Middle East
• The linguistic and other cultural relationships, which Ethiopia shares with
its neighbors, reflect the influence of location.
17

Cont’d . . .
C) Political
 The political history of Ethiopia has been considerably influenced by:
Geopolitical considerations of superpowers.
Adjacency to the Red Sea (a major global trade route).
The Middle East geopolitical paradigms.
 As a result, Ethiopia has been exposed for external invasions in a number
of times; though the country resisted foreign intervention and remains free
of external domination.
d) Size of Ethiopia
 Ethiopia with a total area of approximately 1,106,000 square kilometers is
the 8th largest country in Africa and 25th in the World.
18

Cont’d . . .
• It extends about 1,639 kilometers East-West, and 1,577 kilometers North-
South.
• About 0.7% of the country is covered by water bodies.
Table: Advantages and disadvantages of Ethiopia‟s large size
19

Cont’d . . .
The shape of Ethiopia and its Implication
 Countries of the World have different kinds of shape that can be divided
into five main categories:
1. Compact: Poland, Burundi, Kenya, Uganda
2. Fragmented: Philippines, Indonesia
3. Elongated, Chile, Gambia
4. Perforated: South Africa
5. Protruded. Eretria Myanmar
 These shapes have implications on defense, administration and economic
integration within a country.
20

Cont’d . . .
• Compact shape countries: The distance from the geographic centre of the
state to any of the borders does not vary greatly. It is easier for defence,
socioeconomic and cultural integration.
• Fragmented shape countries: They are
• divided from their other parts by either water, land or other countries. E.g.
Philippines.
21

Cont’d . . .
• Elongated shape countries: They are geographically long and relatively
narrow like Chile.
• Perforated shape countries: A country that completely
surrounds another country like the Republic of South Africa.
• In the Middle there is one independent
• country called Lesotho.
•
• Protrude shape countries: Countries that have one
• portion that is much more elongated than the
• rest of the country like Myanmar and Eritrea.
22

Cont’d . . .
 There are various ways of measuring shape of countries, known as the
indices of compactness.
 It measure the deviation of the shape of a country from a circular shape.
 There are four most commonly used measures of compactness. These
are:
1. The ratio of area of country to its boundary length:
• It is also called Area-Boundary ratio.
• The higher the A/B ratio, the greater the degree of compactness and
the smaller A/B ratio , the lesser the degree of compactness
• A border/area ratio of zero indicates that the country has no land
borders.
23

Cont’d . . .
2. Boundary-Circumference ratio. It measures how far the boundary of a
country approximates the circumference of a circle of its own size.
3. Area-Circumference ratio. It compares the area of the country with the
circumference of a circle that passes touching the extreme points on the
boundary of the country. The higher the A/C ratio, the greater the degree
of compactness.
4. Area-Area (A/A‟) ratio. The area of the inscribing circle is the area of the
smallest possible circle whose circumference passes through the extreme
points on the boundary. The nearer the ratio to 1, the more compact the
country is.
24

Cont’d . . .
Table: Ethiopia's shape compared to its neighbors in the Horn
25

1.3. Basic Skills of Map Reading
• A map is a two-dimensional scaled representation of part or whole of
the Earth surface on a flat body such as piece of paper, black board,
wood or cloth.
• Map reading encompasses a systematic identification of natural
features and manmade features.
• Natural features include mountains, plateaus, hills, valleys, river,
ocean, rocks, plain etc.
• .
26

...con’d
• On the other hand, manmade features include roads,
railway, buildings, dam etc.
• Although many disciplines use maps, they have a special
significance for Geographers as primary tools for displaying
and analyzing spatial distributions, patterns and relations.
• Since these features cannot easily be observed and
interpreted in real landscapes, maps are essential to
Geographers
27

Cont’d . . .
Importance of maps
 Provide the basis for making geographical details of regions represented i.e. the
geographical facts of an area such as relief, drainage, settlement etc.
 Powerful tools for making spatial analysis of geographical facts of areas represented.
 Useful for giving location of geographical features by varied methods of grid reference,
place naming etc.
 Maps are used on various disciplines like land use planning, military science, aviation,
tourism, marine science, population studies, epidemiology, geology, economics, history,
archaeology, agriculture etc.
 Map makes storage of the geographical data of areas represented.
 Maps are potentially used to asses‟ reliable measurements of the geographical features.
The measurements can be of area size, distance etc.
28

Cont’d . . .
Types of Map
 There are many types of maps according to their purpose and functions. For now, only
topographical and statistical maps are considered .
A. Topographical maps: Topographic maps depict one or more natural and cultural features
of an area.
 They could be small, medium or large scale depending on the size of the area
represented.
 Contents of topographical maps depend on purpose of a map, scale of a map, date of
compilation, and nature of the land represented.
B. Special purpose/statistical maps: These are maps, which show distribution of different
aspects such as temperature, rainfall, settlement, vegetation etc.
29

Cont’d . . .
Marginal Information on Maps (Elements of Maps)
 Title, Key, Legend, Scale, North Arrow, Margin, Date of compilation.
Basic Principles of Map Reading
 The first symbols introduced should be those, which refer to landscape
features of which the reader already has some images.
 Secondly, knowledge of directions is an important principle in reading
maps.
 Maps are covered in a series of lines that make up a grid. This
description, which will be a series of numbers, is known as a grid
reference.
30

Basic Principles of Map Reading
• Map Readers must have ideas about the symbol and also
the real World (landscapes).
• Every map symbol must be visualized by the reader to read
a map.
• Land scape features
• The first symbols introduced should be those, which refer to
landscape features of which the reader already has some
images.
• Map symbols should be introduced as needed.
• E.g. Mountains, rivers, lakes
31

…con’d
• Direction
• Secondly, knowledge of directions is an important principle in
reading maps.
• One of the basic functions of maps is to help us to orient ourselves
and to locate places on the earth.
• Unless a reader knows the basic directions, he or she may not use a
map effectively.
• Before locating features using a map, north (the north arrow) should
be determined and the readers should have practice in finding this
direction.
• Next they should learn to read direction on a specific map and the
location of the features shown on the map in relation to one another.
32

...Con’d
• Grid lines
• Maps are covered in a series of lines that make up a grid.
• The lines have numbers accompanying them that allow
you to accurately pinpoint your location on a map.
• Once you have located where you are, the grid system
makes it simple to give an accurate description of your
location.
• This description, which will be a series of numbers, is
known as a grid reference.
33

Review Questions
Answer the following questions briefly.
1. What are the implications of location, shape and size of
Ethiopia and the Horn on the physical environment,
socioeconomic and political aspects?
2. Explain the themes of Geography.
3. What are the basic principles of map reading?
34

Chapter Two
THE GEOLOGY OF ETHIOPIA AND THE HORN
35

Chapter Contents
2.1. Introduction
2.2. The Geologic Processes: Endogenic and Exogenic Forces
2.3. The Geological Time Scale and Age Dating Techniques
2.4. Geological Processes and the Resulting Landforms of Ethiopia and the Horn
2.4.1. The Precambrian Era Geologic Processes (4.5 billion - 600 million years ago)
2.4.2. The Paleozoic Era Geologic Processes (600 million - 225 million years ago)
2.4.3. The Mesozoic Era Geologic Processes (225-70 million years ago)
2.4.4. The Cenozoic Era Geologic Processes (70million years ago - Present)
2.5. Rock and Mineral Resources of Ethiopia
2.5.1. Brief Facts and Current State of Main Minerals in Ethiopia
2.5.2. Mineral Potential Sites of Ethiopia
36

Chapter Two
Chapter Objectives
1. Analyze the geologic processes and the resultant land
forms of Ethiopia and the Horn.
2. Examine the formation of the Rift Valley.
3. Recognize the current status of Ethiopian mineral
endowment associated with geologic processes.
37

38 Hawassa University GeES 1011

2.1. Introduction
• Definition: Geology is an earth science that deals with
the evolution of the earth processes that shape the
earth’s surface.
• Much of Geology is concerned with events that
• took place in the remote past when no one was around to
witness them and
• are far beneath the earth’s surface where no one can see them
• The clues to study Geology includes:
Geophysics: studying earthquake waves
Geochemistry: analysis of the detailed composition of rocks
Geochronology: methods for finding the ages of rocks
39

2.1. Introduction
• The earth’s continents were once bunched up together in to
a single huge continent (Pangaea)
• Pangaea was then split into Gondwanaland where Africa is a
part and Laurasia; and
• later into smaller fragments over the last million years.
• Then gradually drifted apart to form the present
arrangement of continents.
40

41
2.1. Introduction

42
2.1. Introduction

2.1. Introduction
Continental drift Theory
o proposed by an Australian Climatologist Alfred Wegener
o is about the assembling of continents together and formed a
supercontinent
His principal observations includes:
o Fit of the continents
o Match of mountain belts, rock types
o Distribution of fossils
o Paleoclimates
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44
2.1. Introduction

2.2. Geological Processes:Endogenic and Exogenic Forces
• Geology studies of how Earth's materials, structures, processes
and organisms have changed over time
These processes are divided in to two major groups:
1. Internal (Endogenic)
2. External (Exogenic) processes.
45

2.2. Geological Processes…
1. The internal processes (endogenic)
• Are volcanic activity and all tectonic processes like folding,
faulting, rifting, warping & sinking.
• Orogenesis (mountain building) & epeirogenesis (slow rising and
sinking of the landmass)
• These geologic forces build up various landforms such as
mountains, plateaus, depressions, etc
2. The external processes (exogenic),
• Are on the contrary, act upon the deformed landscapes by
sculpturing (smoothing) and leveling.
• The major processes are weathering, denudation, deposition,
peneplanation and mass movement.
• These two forces operate over the surface of the earth and
likely over Ethiopia.
46

2.3. The Geological Time Scale & Age Dating Techniques
• The geological history is divided in to Eras.
• Each Era is divided into periods.
• The Eras are given names that indicate the kind of
life that existed in them
• Example: Paleozoic Era: ancient life
• Cenozoic Era: recent life and so on
47

2.3. The Geological Time Scale …
Geological Time divisions differ one another by:
o relative position of land and sea
o kind of climate
o the kind of animal and plant life
The geological time scale measures time on a scale involving four
main units:
1. An epoch: smallest unit of time on the scale & millions of years
2. Chronologically, epochs are clumped together into larger
units called periods
3. Periods are combined to make subdivisions called Eras
4. An eon is the largest period of geological time
48

...con’d
49

Age Dating Techniques
• Two techniques of knowing the age of rocks:
• Relative and absolute age dating
• Relative Dating
o uses geological evidence to assign comparative ages of fossils
• Two ways of relative dating
• 1. to look at any fossils the rock may contain
• 2. to use the "What is on top of the older rocks?“
• Demerit: these two methods only give the relative age of
rocks -which one is younger and which is older.
50

Absolute Dating
• Also said Radiometric techniques
• was developed with discovery of radioactivity in 1896
• The regular rates of decay for unstable, radioactive elements
were found to constitute virtual “clocks” within the earth’s
rocks
• Examples: Uranium [U] & Thorium [Th]
• Every radioactive element has its own half-life
51

• Two major techniques are:
• Carbon-14 Technique:
• Upon the organism’s death, carbon-14 begins to
disintegrate at a known rate, and no further
replacement of carbon from atmospheric carbon
dioxide can take place.
• Carbon-14 has half-life of 5730 years.
52

B. Potassium-Argon Technique:
o The decay is widely used for dating rocks.
o Geologists are able to date entire rock samples in this
way, because potassium-40 is abundant in micas,
feldspars, and hornblendes.
o Leakage of argon is a problem if the rock has been
exposed to temperatures above 125° C (257° F),
because the age of the rock will then reflect the last
episode of heating rather than the time of original
rock formation.
53

54

2.4. Geological Processes and the Resulting Landforms
of Ethiopia and the Horn
• Since the time of our earth appeared as a planet in the
solar system (about 4.5 billion years ago) four major
geological eras have elapsed/
• There had been different geological & biological events in
these eras.
1. Precambrian era (4.5 billion-600 million years ago )
2. Paleozoic era (600-225 million years ago)
3. The Mesozoic era (225-70 million years ago)
4. Cenozoic Era (70 million years ago – present)
55

2.4. Geological Processes and the Resulting…
a) Precambrian era (4.5 billion-600 million years ago )
• It is the oldest and longest geological era covering 5/6th of the
earth’s geological time scale.
• This era was characterized by repeated Orogenic episodes
(mountain building). i.e. the land was subjected to intense folding &
accompanied by intrusive igneous activity.
• Due to continuous denudation (wearing away) of the covering
rocks, these mountains are reduced to near-level (peneplainned)
rock surfaces.
• the other rocks, forming the basement rocks.
56

• This “leveled” surfaces of the Precambrian era were latter
(in the Mesozoic & Cenozoic eras) covered by younger
rocks formations
• Thus, in most parts of Ethiopia, rocks belonging to
Precambrian era are found beneath all
• Since they have been subjected to pressure and heat from
overlying weight, earth movements (folding, orogenesis) and to
intrusive igneous activity, the original rocks (both sedimentary &
igneous) were altered into metamorphic rocks of varying stages
of metamorphism.
57

• Today, in a few areas of Ethiopia, outcrops of old crystalline
basement complex rocks are found on the surface, due to
continuous denudation.
• Example:
1. In the western Part: Gambella, Benishangul-Gumuz
(Metekel and Asossa), western Gojjam, western Wellega,
Illuababora, and Abay gorge.
2. In the southern Part: Guji, southern Omo, and parts of
southern Bale and Borena.
3. In the eastern part: Eastern Hararghe.
• During Precambrian era structural formation had also taken
place
58

b) Paleozoic era (600-225 million years ago)
• Denudation and peneplanation was the major geological
processes of this era.
• The gigantic mountains that were formed by the Precambrian
orogeny were subjected to intense & prolonged denudation.
• The sediments were transported southward and eastward to form
continental (in Africa) and marine deposits, respectively.
• Because of the limited deposition within Ethiopia, rocks belonging
to this era are rare in the country.
• This was the era when no structural formation (mountain building)
took place.
• The Paleozoic era is known for the predominance of
invertebrates.
59

C) The Mesozoic era (225-70 million years ago)
• The most important geological occurrences of the Mesozoic era in
the Horn were the sinking and uplifting of the landmass
• This era has three periods
60

• In the Triassic Period, the landmass sank due to
internal forces.
• This event was followed by transgression of a nearby
sea into the mainland of today’s Somalia, and
southeastern Ethiopia.
• During the Triassic Period, the oldest sedimentary
rock known as Adigrat sandstone was formed.
61

• In the Jurassic Period, the transgression of the sea
continued into the mainland in the northwest direction.
• This event deposited another sedimentary rock known
as Hintalo limestone.
• In the Cretaceous Period, the landmass began to
rise and the sea started to regress towards the
southeast, depositing sedimentary rock known as
Upper Sandstone.
• Upper Sandstone is the youngest sedimentary rock,
and therefore overlies the rest.
62

• The Mesozoic Era was an era of sedimentary rock formation in
Ethiopia and the Horn.
• The Mesozoic is also known for the predominance of reptiles.
• Huge reptiles, such as dinosaurs, were dominant.
• However, at the end of this era, two other significant
biological events occurred:
• Dinosaurs disappeared, and mammals, birds and flowering
plants emerged.
• Mesozoic rocks are considered to have the greatest
potential for oil and gas deposits
63

64
Figure 2.1. Geological map of Ethiopia Source: CSA Shapefile, 2012

d) Cenozoic Era (70 million years ago – present)
• It is the most recent of the geologic eras.
• The tectonic and volcanic activities that took place in this era
have an important effect in the making of the present-day
landmass of Ethiopia and the surrounding areas.
• Very significant structural, climatic and biological events have
occurred in the Horn
• the uplifting that began in the Cretaceous Period of the
Mesozoic Era continued and reached its maximum height.
65

Major geologic structures events that took place during this time include:
a. Uplifting of the Arabo-Ethiopian landmass and outpouring of huge
quantity of lava.
b. Formation of the Rift Valley.
c. Quaternary volcanism and deposition.
66

a) Tertiary Period (70 million - 2 million years ago)
• In Ethiopia and the Horn it formed huge blocks of dome over the
greater part of the region.
• As the uplifting continued through time, great cracks opened in the
crust and resulted in the pouring out of extensive basaltic lava
(known as the Trappean lava series).
• The lava resulted in the formation of:
• The Eritrean Highlands, The Northwestern Highlands, The
Southeastern Highlands, and The Somali plateaus
• As the cracking continued during the period, it formed the Great
East African Rift Valley System of which the Ethiopian Rift Valley
System is part.
67

• The spatial extents of the Rift Valley
• The Ethiopian Rift valley is part of the Great Rift Valley
distance of about 7200 km.
• Of these 5,600 km is in Africa and 1,700kms in Eritrea and Ethiopia.
• On land, the widest part of the rift valley is the Afar Triangle (200-
300 km)
The formation of the rift valley has the following structural effects.
1. Divide the Ethiopian plateau in to two
2. Separate the Arabian landmass from African landmass
3. Caused the formation of dead sea, Red Sea and Gulf of Aden
troughs
4. Created basins and fault depressions on which the Rift Valley lakes
were formed Hawassa University GeES 1011
69

b) Quaternary Period (2 million - recent years)
In the Quaternary Period, these structures were formed in
Ethiopia:
1. The Afar Horst that extends into Djibouti
2. The active volcano of Ertalle in Afar
3. The dormant volcanic mountain of Fentalle in Eastern Oromia
4. The extensive lava field of Methara.
70

71
.

• b) Quaternary Period (2 million - recent
years)…
• Quaternary volcanism
• known as Aden Volcanoes or Aden Series
• limited to the floor of the Rift Valley and the region
south of Lake Tana
• more extensively developed in the Afar region
• rift valley is still unstable
73

• b) Quaternary Period (2 million - recent years)…
• The basic volcanic features of the Aden series include
the following:
• Numerous and freshly preserved volcanic cones Eg. Dubi,
Erta Ale, Afrera etc. Of these, Erta Ale is the most active volcano
in Ethiopia.
• Volcanic hills and mountains, some of which are semi-
dormant (Fantale, Boseti-Gouda near Adama, Aletu north of
Lake Ziway, Chebbi north of Lake Hawassa etc.).
• Extensive lava fields and lava sheets some of which are very
recent.
• Lava ridges.
• Thermal springs, fumaroles etc
74

• much of the areas (except the high mountains) were
periods of an excessively high rainfall.
• This is called the pluvial period
• which resulted in an excessive surface flow that
carry a lot of sediments and deposited these on the
lower areas
75

According to the place and manner of deposition and depositing
agents these deposits are divided as follow.
a. Lacustrine deposits: Deposits on former lakebeds, and swampy
depressions.
b. Fluvial deposits: Deposits on the banks of rivers, flood plains both in
plateau, foothills etc.
c. Glacio-fluvial deposits and erosional features: These are occurred on
high mountains, such as Bale and Kaka Mountains.
d. Aeolian deposits: Are windblown deposits.
e. Coastal and marine deposits: Deposits on sea invaded and sea-
covered places.
76

77
There were many rivers, lakes & even these lakes merge together e.g.
Ziway-Langano; Awasa-Shalla; Chamo-Abaya; etc.

2.5.Rock & Mineral Resources in Ethiopia
o The occurrence of metallic minerals in Ethiopia is
associated with the Precambrian rocks
o The exploitation and search for mineral deposits in Ethiopia
has a history of > 2,000 years
o However, presently mineral production from Ethiopia has
been negligible by World standards.
78

79
Minerals Main Locations but not limited to
Gold Benishangul-Gumuz (Metekel), Adola,,,
Platinum Yubdo area in Wellega,,,
Tantalum southern Ethiopia, Adola area,,,
Gemstones Amhara and Oromia region,,,
Potash Danakil (Dallol Depression) of
Gypsum and
Anhydrite
Danakil Depression, Ogaden, Shewa
Clay Ambo and Adola,,,
Marble Tigray, Amhara, Oromia
Construction stones Diredawa, Amhara, Tigray,,,

80
Mineral Potential Sites of Ethiopia
1. The Western and South-western-greenstone belt:
Gold, Platinium
2. The Southern greenstone belt: Called Adola Belt:
Primarly gold deposit
3. The Northern greenstone belt(Tigray):
gold deposit
2.5.Rock & Mineral Resources in Ethiopia…

Chapter review questions
1. What were the major geologic processes of the
Precambrian and Paleozoic Eras in the Horn of
Africa?
2. Explain the formation of the oldest sedimentary
rocks in Ethiopia and the Horn.
3. Discuss the major geologic events of Ethiopia
that took place during the Cenozoic Era.
4. Where are the major mineral potential sites of
Ethiopia? Discuss each of them with the help of
examples.
81

Chapter Contents
3.1. Introduction
3.2. The Physiographic Divisions of Ethiopia
3.2.1. The Western Highlands and Lowlands
3.2.2. The Southeastern Highlands and Lowlands
3.2.3. The Rift Valley
3.3. The Impacts of Relief on Biophysical and
Socioeconomic Conditions
Review Questions
83

Chapter Objectives
• Describe the topography of Ethiopia and the Horn.
• Identify the physiographic divisions of Ethiopia.
• Elucidate the physiographic characteristics of the Rift
Valley.
• Explain the impacts of relief on biophysical and
socioeconomic conditions
84

3.1. Introduction
• The topography of Ethiopia is largely determined by the geologic
activities of the Cenozoic Era.
• The uplifting of the Arabo-Ethiopian swell and the subsequent
outpouring, spreading and thick accumulation of Trapean lava have
given rise to an outward sloping highland plateau and mountains.
• The major faulting resulted in the division of the plateau into two
broad units and the formation of a great structural valley.
• Faulting elsewhere and on the floor guided part of the course of
some rivers.
• They also formed depressions on which lakes were subsequently
created.
• Geomorphic processes brought some modification to the structural
landform by river dissection and roughening on the highlands, and
deposition on the lower areas.
85

3.1. Introduction
• The Ethiopia’s topography is characterized by great diversity
• flat-topped plateaus, high and rugged mountains, deep river
gorges and vast plains
• Altitude ranges from 125 meters below sea level (Kobar Sink) to
4620m amsl (Ras-Dashen).
• Ethiopia has the largest proportion of elevated landmass in the
African continent.
• More than 50% of the Ethiopian landmass is above 1,000
meters of elevation; and above 1,500 meters makes 44% of
the country.
• Because of this, Ethiopia is said to be the “roof of eastern
Africa.”
86

General Characteristics of the Ethiopian
Physiography
• Most of the Ethiopian Highlands are part of
central and northern Ethiopia, and its
northernmost portion extends into Eritrea.
• the most significant physical features of the
country, which form the largest continuous
area of its elevation in the continent.
• Dissected by rivers and deep gorges
• Divided into several mountains and plateau
that can be the source of many rivers
• As a result, Ethiopian plateau is called “the
water tower of north east Africa.”
87

General Characteristics of the Ethiopian
Physiography
• The diversity in topography is accompanied by differences in other
natural features such as soil, climate, vegetation and wild life as well
as socio-cultural and economic phenomena.
• 1000m is considered as a demarcation between highlands and
lowlands
• The cumulative effect of all this is that, the highlands have been
significant throughout Ethiopian history in the economic, cultural and
political life of the people.
• These highlands make up nearly 56% of the area of the
Ethiopia.
• This is further subdivided into lower highland (1,000 - 2,000
m.a.s.l), which make up 35% and higher highland (>2,000
m.a.s.l) constituting nearly 22%.
88

highlands
• Moderate and high
amount of rainfall (>600
mm per year).
• Lower mean annual
temperature (<200C).
• The climate is favorable for
biotic life.
• Rain-fed agriculture is
possible.
• Free from tropical diseases.
• Attractive for human
habitation and densely
settled.
lowlands
• Fewer amounts of rainfall
and higher temperature.
• High prevalence of tropical
diseases.
• Lower population densities.
• Nomadic and semi-
nomadic economic life.
• Vast plain lands favorable
for irrigation agriculture
along the lower river basins.
Characteristics of Highlands vs Lowlands
89

3.2. The Physiographic Divisions of Ethiopia
• Following the structural divisions brought about by the
geologic processes of the Cenozoic Era, three major
physiographic units can be identified in Ethiopia.
• These are:
• The Western highlands and lowlands
• The South-eastern (Eastern) highlands and lowlands
• The Rift Valley
90

Elevation in Ethiopia
91

The Western Highlands and Lowlands
• includes all the area west of the Rift Valley.
• It extends from north to south encompassing nearly the
whole western half of Ethiopia.
• makes up about 44% of the area of the country.
• In the east the western escarpment of the Rift Valley bound
it whereas westward, the land gradually descends in
altitude until it merges into the western foothills and
lowlands, along the Sudan and South Sudan border.
• further subdivided into four groups of highlands (76.3%) and
four groups of lowlands (23.7%).
92

The Ethiopian Topography
93

Western highlands
Western highlands
Tigray plateau
North central
Massifs
The Shewa
Plateau/central
highlands
Southwestern
highlands
94

A. Tigray plateau
• extends from the Tekeze gorge in the south to central
Eritrean highlands.
• separated from the Eritrean plateau by the Mereb
River
• constitutes about 13% of the area of the region.
• elongated highland with most of the land being in
between 1,000 and 2,000 meters above sea level.
• The right bank tributaries of Tekeze drain this
plateau.
• Long period of denudation has created residual
features of granite hills, rugged topography, and
Ambas.
95

Continued
• There are high mountains in this
plateau with elevations of over
3000 meters, namely
• Mount Tsibet (3988 m.a.s.l)
• Mount Ambalage (3291
m.a.s.l), and
• Mount Assimba (3248 m.a.s.l).
• famous monastery at Debre-
Damo, a tableland that can only
be climbed by a rope pulley is
located in this region Mt
Ambalage
96

B. North Central massifs
• the largest in the western highlands.
• Much of its northern and southern limit follows the Abay and
Tekeze gorges.
• The Abay, Tekeze and their tributaries have cut into this region
a maze of gorges, steep sided river valleys, dividing the land
into many isolated plateau blocks, precipitous tablelands and
other rugged surface forms.
• But much of these plateau and tablelands are still capped by
the Trappean lava.
• In its central part, the physiographic unit also accommodates
the Lake Tana basin surrounded by plains of Fogera and
Dembia in the north and an upland plain in its south.
97

North… continued
• Fifty-eight percent of the region is at an altitude of more than 2,000 meters,
making it, next to the Shewan Plateau, the second highest physiographic
division.
• The region consists of the Gonder, Wello and Gojjam Massifs.
• Out of the 26 mountain peaks with altitude of more than 4,000m.a.s.l in
Ethiopia, 19 mountain peaks are found in this physiographic region.
• Among these, the most popular ones include
• Mount Ras Dashen (4,620 m.a.s.l),
• Mount Weynobar/Ancua (4462 m.a.s.l),
• Mount KidisYared (4453 m.a.s.l), and
• Mount Bwahit (4437 m.a.s.l) in the Simen Mountain System.
• Mount Guna (4,231m.a.s.l) in the Debre Tabour Mountain System,
• Abune Yoseph (4,260 m.a.s.l) in the Lasta highlands of Wello and
• Mount Birhan (4,154 m.a.s.l) in the Choke Mountain System
98

North… Continued
• The Mountain systems in Gonder and Gojjam are separated from
the eastern group of mountains in Wello by impenetrable and deep
gorges.
• At one point though, they are connected by Yeju-Wadla Delanta
land bridge (ridge).
• This land bridge has been significant in history.
• served as a route of penetration by the Turks, Portuguese, and
Italians etc.
• The Woreta-Debre Tabor-Woldya road constructed to link the
northwestern region with Asseb through Woldya and Dessie
took advantage of this land bridge.
99

C. The Shewa Plateau/central highlands
• bounded by the Rift Valley in the east and southeast, by
the Abay gorge in its northern and western limit, and the
Omo gorge in the south and west.
• occupies a central geographical position in Ethiopia.
• With only 11% of the area of the whole physiographic
region, the Shewa Plateau is the smallest of the Western
highlands.
• Nearly three fourth of its area is at an altitude of more than
2,000 meters above sea level.
• It has, therefore, the largest proportion of elevated ground.
100

C. Shewan…. continued
• Drained by the tributaries of Abbay, Omo and Awash
• The tributaries of
• Abay Guder,
• Muger,
• Jema etc. have cut deep gorges and steep sided river
valleys.
• Omo and Awash have dissected the other sides of the
plateau.
• The highest mountain in the Shewan plateau is
• Mount Abuye-Meda (4,000 m.a.s.l) in Northern Shewa,
• Mount Guraghe in the south is 3,721 meters high.
101

D. The Southwestern Highlands
• consists of the highlands of Wellega, Illuababora, Jimma,
Kaffa, Gamo and Gofa.
• separated from the adjacent highlands by the Abay and
Omo river valleys.
• extends from the Abay gorge in the north to the Kenya
border and Chew Bahir in the south.
• accounts for 22.7% of the area of the region.
• is the second largest in the Western highlands.
• About 70% of its area is lies within 1,000-2,000 meters
altitude.
102

D. South… continued
• The southwestern plateau is the wettest in Ethiopia.
• It is drained by
• Dabus
• Deddessa (tributaries of Abay),
• Baro,
• Akobo and the Ghibe/Omo rivers.
• The numerous streams have cut these highlands to produce
the most dissected and rugged terrain that accommodates
the most numerous and diverse ethnic linguistic groups in
Ethiopia.
• With a height of 4,200 meters above sea level, Guge Mountain is
the highest peak in this physiographic subdivision.
103

The Western Lowlands
• western foothills and border plains that extend from
Western Tigray in the north to southern Gamo-Gofa in the
South.
• In certain places, ridges or part of the highlands protrude
into the lowlands, interrupting their continuity.
• They make 11% of the area of the physiographic region.
• The general elevation ranges between 500 and 1000
meters above sea level.
104

Continued
Western
lowlands
Tekezze
lowlands
Abay-
Dinder
lowlands
Baro-Akobo
lowlands
Ghibe
lowlands
It can be subdivided into four categories
105

Continued
• With the exception of the Baro lowland, the region is generally
characterized by arid or semi-arid conditions.
• Pastoral or semi-pastoral economic activities dominate the area.
• As one moves northwards, the degree of aridity increases,
making rain-fed agriculture more difficult.
• Since one or two rivers cross all of these lowlands, irrigation
agriculture is highly feasible.
• For example, the Baro lowland has an extensive flat area suitable
for mechanized agriculture.
106

…con’d
• The Ghibe/Omo lowland, which includes the lower Ghibe/Omo
Valley and the northern section of the Turkana basin, is
classified in the Western lowlands from its geographical
location.
• But structurally it also belongs to the Rift Valley.
• It is an area, which is both faulted and tectonically
depressed.
• In the Western lowlands, there are small but important towns.
• Their importance could be related to agriculture, history, or
are simply border towns and frontier ports.
• These are Humera, Metema, Omedla, Kurmuk,
Gambella etc.
107

The Southeastern Highlands and Lowlands
• South east highlands
• Arsi- Bale-Sidama
• Hararghe Plateau
• South eastern Lowlands
• Ogaden
• Elkerie
• Borena
108

…con’d
• A. Arsi-Bale-Sidama Highlands
• the second largest in terms of area.
• accounts for 37% of the area of Ethiopia.
• The highlands make up 46% of the physiographic division while
the rest is lowland.
• In the west and north, the eastern escarpment of the Rift Valley
makes the western and northern limit.
• land raises so abruptly that from the edge of the plateau one
literally looks down the Rift Valley.
• the land gradually descends southeastward
• further subdivided into
• two units of highlands and
• two units of extensive lowlands.
109

Continued…
• are found to the east of the Lakes Region.
• They are located in the south western section of the
physiographic region.
• make up 28.5% of the area of the region and 62% of
the south - Eastern Highlands.
• The Arsi Highlands are made up of flat rolling uplands
and dissected mountains.
• The well-known mountains in this area are
• Mount Kaka (4,180 m.a.s.l),
• Mount Bada (4,139 m.a.s.l) and
• Mount Chilalo (4,036 m.a.s.l).
110

Continued…
• The Bale highlands are separated from the Arsi highlands by
the head and main stream of Wabishebelle.
• They consist of a platform looking basaltic plateau in the north-
central part and high mountain massif to the south.
• The Afro-Alpine summit of Senetti plateau is found on the latter
group.
• The highest mountain peaks in this region are Tulu-Dimtu
(4,377 m.a.s.l) and Mount Batu (4,307 m.a.s.l).
• Erosion features belonging to Pleistocene glaciation but later
modified by fluvial processes
• The Arsi-Bale Highlands are important grains producing areas
with still high potential.
111

…con’d
• The Sidama Highlands are separated from the Bale
Highlands by the Ghenale river valley.
• occupy the southwestern corner of this region.
• The prominent feature here is the Jemjem plateau, an
important coffee growing area.
• Rivers Wabishebelle and Ghenale along with their
tributaries have dissected this physiographic region.
• Specially, Weyb River, tributary of Ghenale, has cut an
underground passage (Sof Omar cave) through the
Mesozoic Limestone rocks.
• The cave is found near Bale Mountains.
• It is one of the World's most spectacular and extensive
underground caverns creating a magnificent view
accessible only by an underground stream.
112

The Hararghe Plateau
• is a north-easterly extension of the south-eastern highlands.
• It extends from the Chercher highlands in the south-west to
Jigjiga in the east.
• It makes up 38% of the South Eastern highlands and 17.4% of
the whole physiographic region.
• It has the smallest proportion of upper highland (>2,000
meters).
• It is a low lying and elongated region.
113

Hararghean plateau
• Rising sharply from the Rift Valley floor,
it immediately but gently descends east
and southeastward.
• The left-bank tributaries of Wabishebelle
drain it.
• Much of the Trappean lava is removed
and the Mesozoic rocks are extensively
exposed.
• The highest mountain here is Mount
Gara-Muleta (3,381 m.a.s.l).
114

The Southeastern Lowlands
• located in the southeastern part of the country and they are the
most extensive lowlands in Ethiopia.
• make up 54% of the area of the physiographic region and
around one-fifth of the country.
• divided into Wabishebelle plain (60%) and the Ghenale Plain
(40%).
• include the plains of Ogaden, Elkere, and Borena.
Southeastward sloping plains characterize these lowlands.
• These extensive plains are interrupted here and there, by low
hills, low ridges, inselbergs and by shallow and broad river
valleys and depressions.
115

…con’d
• Because of the harsh climatic conditions, these
lowlands are little used and support very small
population.
• They are sparsely inhabited by pastoral and semi-
pastoral communities.
• The economic potential for this region includes animal
husbandry, irrigation, agriculture and perhaps
exploitation of petroleum and natural gas.
116

…con’d
• The Rift Valley is a tectonically formed structural
depression.
• It is bounded by two major and more or less parallel
escarpments.
• The formation of the Rift Valley has separated the
Ethiopian Highlands and Lowlands in to two.
• It extends from the Afar triangle in the north to Chew Bahir
for about 1,700 km2.
• It covers 18% of the area of Ethiopia.
• It is elongated and funnel shaped, with a NE-SW
orientation.
• It opens out in the Afar Triangle, where it is the widest, and
narrows down to the south.
117

…con’d
• The floor of the Rift Valley is made up of interconnected troughs,
grabens and depressions.
• Volcanic rocks, fluvial and lacustrine deposits cover the floor.
• In many places, numerous volcanic domes, hills and cinder cones rise
from the floor.
• Altitude in the floor ranges from 125 meters below sea level at Dallol
Depression, to as high as 2,000 meters above sea level in the Lakes
region.
• The bounding escarpments are also of varying heights.
• From the floor to the edge of the escarpment, the heights vary from
200 to 1500 meters.
• Because of its altitudinal variation and positional differences, the
climate also varies from warm, hot and dry to cool and moderately
moist conditions.
118

…con’d
• Similarly, the social and economic life reflects this pattern.
• There are places, which are desolate and sparsely inhabited by
pastoralists where as in others parts people practice some rain-fed
agriculture.
• The Rift Valley is further subdivided into three physiographic sub-
regions.
• the Afar Triangle,
• the Main Ethiopian Rift, and
• the Chew Bahir Rift
119

Afar Triangle
• The Afar Triangle is the largest and widest part of the Rift
Valley. It makes up 54% of the Rift Valley area.
• It is bounded by the high western and eastern escarpments
in the west and east respectively, and by the Afar and
Aisha Horst in the northeast.
• The area is generally of low altitude (300-700 meters).
• Quite different is the morphology of the Afar depression,
triangular-shape lowland, where elevation drops uniformly
from approximately 1,000 meters in the southwest to below
sea level in the north (Danakil depression) and in the east,
where the shores of Lake Asal, fluctuating at around 125
meters below sea level, represent the lowest subaerial
point of the African continent.
120

…con’d
• The depression, which hosts one of the most hostile
environments on Earth (maximum temperatures can exceed
50°C during the summer wet season; Dallol, at the northern tip
of Afar.
• It is characterized by
• faulted depressions (grabens), volcanic hills, active volcanoes,
volcanic ridges, lava fields and low lava platforms
• Lakes (Abe, Asale, and Afrera)
• Denakil Depression (Kobar Sink).
• Salt plain
• Hot and dry climate
• The economic importance of this region includes salt extraction,
irrigation along the Awash River and electric potential from
geothermal energy.
121

The Main Ethiopian Rift/Central Rift
• it refers to the narrow belt of the Rift Valley
that extends from Awash River in the north to
Lake Chamo in the south.
• It is bounded by the western and eastern
escarpments.
• With the exception of the Arba-minch area,
the bounding escarpments are generally low.
• This part of the Rift Valley is the narrowest
and the highest.
• It has an average width of 50-80 kilometers
and general elevation of 1,000-2,000 meters
above sea level.
122

…con’d
• The floor in many places is dotted by cinder cones and
volcanic mountains.
• The big ones include Mount Fentale, Boseti-guda (near
Adama), Aletu (north of Lake Ziway) and Chebi (north of
Lake Hawasa).
• The northern section has more of these cinder cones and
lava fields.
• The prominent features, however, are the numerous lakes
formed on tectonic sags and fault depressions.
• It is mild and wet, people practices rain-fed agriculture,
recreational value of the lakes, the agricultural importance of
some streams and lakes, and the geothermal energy potential.
123

The Chew Bahir Rift
• This is the smallest and the southern-most part
of the Rift Valley.
• Gneissic highlands of Konso and the surrounding
highlands separate it from the Main Ethiopian
Rift to the north.
• The characteristic feature of this region is the
broad and shallow depression, which is a marshy
area covered by tall grass, into which the Segen
and Woito streams empty.
124

3.3. The Impacts of Relief on Biophysical and
Socioeconomic Conditions
• Ethiopia’s topography has influence on the various socioeconomic
aspects of Ethiopia
1. Agricultural practices
• Choice of farming techniques and farm implements are highly
influenced by relief
• crop production
• as some corps are well adapted to higher altitudes (barley,
wheat) and others to low altitude (sorghum, maize).
• The practice of animal husbandry
• most equines and sheep are reared in the higher altitudes
and camels and goat are well adapted to lower altitudes
125

…con’d
2. Settlement pattern
• Highlands of Ethiopia that experience a temperate type
of climatic condition that are mainly free from most of
the tropical diseases are densely settled.
• Rugged and difficult terrain hinders the development of
settlement and its expansion.
• The highlands of Ethiopia are characterized by
sedentary life and permanent settlements while
lowlands that are inhabited by pastoralists have
temporary settlements.
126

…con’d
3 Transportation and communication
• The highly dissected nature of the landscape is a
barrier to the development of internal surface
transportation that resulted in the long-term isolation of
many communities
• The difficult terrain makes infrastructure development
and maintenance costly.
• TV and radio communications are also highly
influenced by relief.
• The rugged topography rendered rivers less navigable
due to the waterfalls, deep gorges and steep cliffs.
127

…con’d
4. Hydroelectric power potential
• The great difference in altitude coupled with high rainfall created
suitable conditions for a very high potential for the production of
hydroelectric power in Ethiopia.
5. Socio-cultural feeling
• The rugged terrain as a result of excessive surface dissection
resulted in the long-term isolation of communities that led to the
occurrence of cultural diversity.
• People who live in the highlands have been identifying
themselves as degegnas (mountaineers) and those who live in
the lowlands as kollegnas (lowlanders).
128

…con’d
6. Impacts on climate
• The climate of Ethiopia is a result of the tropical position of
the country and the great altitudinal variation of the general
topography.
• Highlands with higher amount of rainfall and lower rate of
evapo-transpiration tend to be moisture surplus compared
to the moisture deficit lowlands.
7. Impacts on soil
• Steep mountain slopes provide low angle of rest, unstable
surface materials and subject to degradation processes
and relatively form shallow and little developed soils.
8. Impacts on natural vegetation
• Relief through its effect on climate and hydrology affect the
type of natural vegetation grown in an area
129

Review Questions
1. What are the three Physiographic Divisions of
Ethiopia
2. What are the impacts of relief on the biophysical
and socioeconomic conditions of Ethiopia?
3. Discuss the physiographic characteristics of the
southeastern highlands and lowlands.
130

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